Automatic temperature control for electric coffee makers



Emperafure Dec. 19, 1944. WOODMAN 2,365,615

AUTOMATIC TEMPERATURE CONTROL FOR ELECTRIC COFFEE MAKERS Filed Sept. 17,1941 INVENTOR A0flfh Moog mar).

' ATTORNEY Patented Dec. 19,

AUTOMATIC TEMPERATURE CONTROL FOR ELECTRIC COFFEE MAKERS Kenneth L.Woodman, Mansfield, Ohio, asslgnor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application September 1'7, 1941, Serial No. 411,112

7 Claims.

My invention relates to electric percolators and, more particularly, toan automatic temperature control for electric percolators.

It is an object of my invention to provide a control for an electriccoffee maker or percolator which will automatically cause the heatingelement to provide a high or coffee brewing temperature and then toautomatically reduce the heat output of the heating element to suchvalue that it will maintain the brewed coffee at a serving temperaturesubstantially below that of the brewing temperature.

It is a further object of my invention to provide a coffee maker orpercolator heating stand having a thermostatic structure therein, inheat relationship with a heating element, which is adapted toautomatically control the output of such heating element for producing ahigh heat output for a predetermined time and then to produce asubstantially lower heat output as long as the heatingelement isconnected to a suitable power supply.

It is another object of my invention to provide a simple, inexpensivecoffee maker or percolator heating stand which embodies an automatictemperature control structure for maintaining a brewing temperaturethroughout a predetermined selective time depending uponthe quantity ofcoffee to be brewed and for automatically reducing the temperature ofsuch coffee so as to maintain it at a desired temperature.

It is still another object of my invention to provide a control for anelectric coffee maker which will cause the heating element to provide ahigh heat output during a predetermined liquid heating period,deenergize the heating element for a predetermined time period to permitproper infusion of the coffee, and intermittently energize the heatingelement to maintain a predetermined low heat output thereafter.

It is still a further object of my invention to provide a heater controlfor a coffee maker having a lower vessel for receiving water and anupper vessel for receiving coffee grounds, which controls theenergization of the heating element to provide a high heat for apreselected time, depending upon the quantity of coffee to be brewed, toproduce the necessary pressure within the lower vessel so as to forcesuch water upwardly into the upper vessel for infusion, whichdeenergizes the heating element when the liquid has been evacuated fromthe lower vessel and elevated into the upper vessel permitting thecoffee to be brewed within the upper vessel, and which upon thecompletion of such infusion period and the return of the brew to thelower vessel intermittently reenergizes the heating element to maintainsuch brew at the desired serving temperature.

It is still a further object of my invention to provide a percolatorheating stand having a thermostatic control for regulating the heatoutput of a heating element incorporated therewith which has adjustablecontrol means operable by an operator, whereby when the coffee hasbrewed a desired length of time, such control means may be operated soas to permit the thermostatic structure to maintain the temperature ofsuch brewed coffee at a predetermined serving temperature.

Yet another object of my invention is to provide a percolator having aheating unit in which the infusion time of the percolator is a functionof the thermal storage capacity of the heating unit and the rate ofcooling thereof.

Other objects of my invention will either be pointed out specifically inthe course of the following description of a device embodying myinvention, or will be apparent from the description taken in conjunctionwith the accompanying drawing, in which:

Figure l is an elevational view partly in section of a coifee makerincorporated with a heating stand embodying my invention;

Fig. 2 is a partial sectional view taken along the line IIII of Fig. 4;I

Fig. 3 is a partial plan view of the heating stand of Fig. 2;

Fig. 4 is an enlarged sectional view of the heating stand embodying myinvention taken along the line IV-IV of Fig. 1;

Fig. 5 is a graphhaving curves illustrating the operatingcharacteristics of the heating element and thermostatic controlembodying my invention;

Fig. 6 is a view similar to Fig. 2 illustrating a modified form of myinvention; and

Fig. '7 is a partial side view taken along the line VII-VII of Fig. 6.

Referring to the accompanying drawing, in which like referencecharacters indicate like parts in the several figures, there isillustrated a coffee maker or percolator which may be of any well knowntype In having a heating stand [2 which comprises an exterior casing it,a heating unit l5, and a thermostatic structure I8 responsive to theheat developed by the heating unit l5 for regulating the operation ofsuch element.

The thermostatic structure It comprises a first heat responsive device2|, a second heat responsive device 22, and a control means 24 therefor.

The coifee maker ,or percolator II, which may be of any well known type.has a lower vessel which rests upon the heating stand l2 in directcontact with the heating unit II for a purpose hereinafter described andan upper vessel which is adaptedrthrough the agency of a asket totightly fit within such lower vessel.

The lower vessel normally retains water to be heated, while the uppervessel is adapted to retain the ground coffee in keeping withestablished practice. The water or liquid in the lower vessel is forcedupwardly, due tothe increaseinpressure therein as such liquid is heated,say, by means of applicants heating stand l2, into the upper vessel, inwhich place infusion with the ground coffee or grounds takes place, in awell known manner. The temperature of the lower vessel is then loweredto permit the passage of the brewed coffee back down into the lowervessel, as hereinafter described.

The heating stand 12 comprises, in this instance, a substantiallycylindrically shaped casing it having a centrally depressed top portionI! which receives the heating unit II and a bottom plate 2l extendingacross the bottom portion of and attached to said casing II. Theexterior casing I4 is preferably formed of any light weight sheetmaterial. A plurality of apertures 23 and 25 are located within the topportion is and bottom plate 2|, respectively, to provide a passage forthe flow of air through the heating stand I2 and about the heating unitI! for cooling said unit, as hereinafter described.

The heating unit I! comprises, in this instance, a flat plate ordisc-shaped member l1 formed of an insulating material, such asporceiain, having spiral grooves in its upper surface for receivingsuitable electrical resistance heating elements 16. The flat insulatingbrick or plate i1 is retained slightly above the top surface of the topportion is of the casing II to permit air passing through said casing tocome in contact with said plate-to cool it as hereinafter described. Theresistance element ii of the heating unit II is connected to a suitablepower supply, not hown, by means of well known prong receptacle members26 and is connected in series with the thermostatic structure II whichis in thermal communication therewith.

The thermostatic structure l| embodies the first heat responsive device2| and the second heat responsive device 22 which are rigidly attachedto a heat conducting supporting bracket 28 which is attached to thedepressed top portion l9 and to the bottom plate 2| of the casing I4.The bracket 2| is formed of good heat conducting material and is rigidlyattached, say, by spot welding, to the top portion IQ of the casing IIwhich, in turn, supports the heating element i6. The bracket 2|,therefore, provides a good heat conducting path from the heating unit lto the thermostatic structure II. The thermostatic structure l| thusreceives its heat from the heating unit and not directly from the lowervessel, and through the variations in temper ture of such heating unitcontrols the operations thereof.

The first heat responsive device 2| is, in this instance, a snap actingbimetallic element, preferably of the type disclosed in the ValvendePatent 1,980,167. Said element is rigidly attached at one end thereof tothe heat conducting bracket 28 by means of a suitable supporting membera (see m. 2). The bimetallic element or am heatresponsivedevice2|hasanadiustableopening temperature. However, the closing temperatureof element 2| runains substantially below that of the servingtemperature of the brewed cofiee and somewhat above the roomtemperature. Accordingly, the thermostatic element 2| will always be ina closed position at room temperature. However, it will remain openwhile the brewed coffee is at the serving temperature. The bimetallicelement or first heat responsive device 2| has a centrally locatedstud-like member 22 rigidly attached thereto for receiving theadiustable control means 2|, as hereinafter described. In addition, amovable plunger member 2| is attached to the movable end of such elementfor engaging the second heat responsive device 22 for a purposehereinafter de scribed.

The second heat responsive member 22 comprises, in this instance, anelongated plain striptype bimetallic member located intermediate thefirst bimetallic member 2| and the supporting bracket 2|. The bimetallicmember 22 is rigidly attached to the bracket 2| at one end by thesupporting bracket 2|. The second bimetallic member 22 operates in anormal manner flexing open and closed so as to maintain the brewedcoffee at its serving temperature. However, member 22 opens at a lowertemperature and develops less flexing power than member 2|, for apurpose hereinafter described. A loosely mounted Jumper member 2| isattached to the movable end of the bimetallic element 22 so as to engagestationary contacts 2| to energize or deenergize the heating unit II ina' manner here inafter described. 1

The first and second bimetallic members 2| and 22, respectively, arepositioned substantially 40 in line with each other so that, when thefirst member 2| which develops a greater flexing force than the secondelement 22, is in its closed podtion, the plunger member 34, attached tothe first member, will engage and retain the second bimetallic member ina contact closed or engaged position, until the first bimetallic membersnaps to its open or high heat position. Accordingly, it follows thatsince the flexing force of the second bimetallic element 22 is somewhatless than that of the first bimetallic element 2| the first bimetallicelement 2| controls or determines the position maintained by the secondbimetallic element.

The manual control or adjusting means 2| comprises, in this instance, anelongated shaft 2| having an inner threaded end portion which threadedlyengages the member 32 attached to the element 20. A control knob 4|positioned outside the casing I4 is attached to the outer end of shaft3| whereby the operator may selectively determine the rotative positionof the shaft 2|. As the control knob II is rotated by an operator, theshaft 2| through its threaded engagement with member 32 determines thelongitudinal position of member 22 and of the midpoint of the bimetallicelement 2|. This selective positioning of the midpoint of element 2|determines or varies the opening temperature of such element, inaccordance with well known teachings, and, in turn, as hereinafterdescribed, controls the operation of the coffee-making process.

When operating the coffee maker heater stand are positioned thereon in amanner similar to that illustrated in Fig. 1. Water is first placedwithin the lower vessel and the coffee bean or grounds within the uppervessel, with the lower vessel being sealed by the upper vessel and itsgasket in a well known manner. The heating unit I! is then connected toa suitable power supply (not shown) by means of any well known cord andplug arrangement, also not shown. The heating unit l thus, upon heating,increases the temperature of the lower vessel and the fluid therein.Inasmuch as the thermostatic structure is initially at room temperaturesuch structure is in a closed or contact engaged position, due to thefirst thermostatic element 20 being in its closed or low temperatureposition, similar to that shown in Fig. 2. The heating unit uponcontinued operation increases the temperature of the liquid in the lowervessel until the increasing pressure produced by the heated liquidforces such liquid upwardly into the upper vessel, in a well knownmanner. The heat output of the heating unit at the time the liquid movesinto the upper vessel is of such value as to cause the firstthermostatic element 20 to snap to its open position. The heating unitI5 is then deenergized, inasmuch as the second bimetallic element 22opens at a lower temperature and, accordingly, opens with the firstbimetallic element 20. It is to be understood that the control knob 40,and, therefore the thermostat 20 are selectively adjustable by anoperator to correspond to the quantity of water in the lower vessel.Accordingly, the temperature required for causing the first element 20to operate will vary with the amount of liquid positioned within thelower vessel. In other words, the operator after having placed apredetermined amount of water within the lower vessel, say, for example,six cups, then rotates the dial 40 to the six-cup position (see Fig. 3).The heat output of the heating unit I5 is thus of such character as tojust raise subthe faster transmission of heat from the unit I! to thesmall mount of liquid remaining in the bottom vessel and the fasterdissipation of this heat by the vaporization of the liquid than the mereradiation of heat from the unit I! and coffee vessel when the vessel isremoved from the unit.

Accordingly, by leaving the bottom vessel in direct contact with theheating unit plate H, by controlling the weight of said plate, andsecuring circulation of air on the bottom and sides of the heater plate(see arrows Fig. 4 which represent the flow of air through the heatingstand H), the infusion time may be accurately controlled. A shortinfusion period may thus be acquired so as to obtain the optimum incoffee making efficiency.

Referring to Fig. 5, I show a temperaturetime curve of the thermostaticstructure I! and bimetallic elements 20 and 22, illustrated by curve OX,and of the water positioned within the lower vessel, illustrated by thecurves 0R. With the six-cup setting of the control knob 40, ashereinabove described, the bimetallic elements increase in temperaturealong the line OK to a temperature as illustrated by the dotted line E,at which point the thermostat 20 will snap open,

' deenergizing the heating element. At this time stantially six-cupsofliquid to the upper vessel by the time the first bimetallic elementsnaps open.

If it be desired to have either a weak or strong coffee, the controlknob 40 may be positioned either below or above the six-cup position,respectively. This, in turn, regulates the temperature of the liquid inthe lower vessel and, accordingly, the pressure produced thereby.

With the liquid elevated to the upper position, infusion takes placewith the coffee bean or grounds. Then as the temperature of the lowervessel and heating element decrease the brewed coffee descends to thelower vessel. The first bimetallic element 20, being capable ofreturning to its closed position only at a point below the servingtemperature, remains open. However, the second thermostatic element 22oscillates between its open and closed position independent of the firstelement 20 so as to maintain the heat output of the heating unit ii atsuch value as to maintain the coffee temperature at its servingtemperature of, say, substantially 175 Fahrenheit.

The infusion time is a function of the thermal storage capacity of theheating unit I5 and the rate of cooling thereof. The infusion timeshould be as short as possible for a good coffee brew. To reduce theinfusion time period to a minimum, the lower vessel is left in directcontact with the heater. By leaving the lower vessel in contact with theplate I! of the heating unit I! said structures cool faster than whenthe vessel is raised above the heating unit. This is due to thetemperature of the water is substantially above that of the servingtemperature, as illustrated by curve OR and dotted line Z, and will havepassed into the upper vessel. Due to the thermal storage capacity of theheating unit including the porcelain plate I! as well as that of thelower vessel of the percolator ID, a predetermined time B will passbetween said de-. energization of the heating element, and thereenergization of the heating element due to the closing of the secondbimetallic element 22. During this "infusion time B the fluid in theupper vessel cools and returnsto the lower vessel.

I After the second bimetallic element 22 has become reengaged, suchelement intermittently energizes the heating element 16 which maintainsthe temperature of the bimetallic elements 20 and 22 at that illustratedby Y on Fig. 5. This, in turn, maintains the temperature of the brewedcoffee at substantially that illustrated by the dotted line Z or thecurve 0R.

It is, therefore, obvious that the described thermostatic controlmechanism for a coffee maker stand provides automatic means for heatingthe water within a coffee maker up to its brewing temperature, and,then, after a predetermined infusion or brewing period, automaticallyregulates the energization of the heating element to maintain the brewedcoffee at a predetermined serving temperature.

Referring to Figs. 6 and 7, a modified form of thermostatic controlstructure l8a embodying my invention is illustrated. As will be noted, asingle thermostatic element, namely, the heretofore so-called secondbimetallic element 22, is employed. However, the control means Zia has acam shaped member 3| attached to the inner end of the control shaft 38.The cam 3| is adapted to engage a pin 21 rigidly attached tosubstantially the midpoint of a bimetallic element 22. The cam 3|engaging the pin 21 retains the bimetallic element 22 in its contactengagement or closed position during the time the heating element isinitially energized or during the time in which the unbrewed water isinitially within the lower vessel. Then, as the water moves from thelower vessel to the upper vesselsoastopermitintusionotthebrewtherein,the operator merely rotates the control knob ll so as to permit thebimetallic element 22 to operate in its normal manner. Such bimetallicelement thus permits the temperature of the heating element It to returnto substantially that illustrated by the dotted line Y in Fig. 5, duringthe infusion period B, whereupon the bimetallic element 21 maintains theenergization of the heating element so as to insure the temperature ofthe brewed coffee being retained at substantially the servingtemperature illustrated by dotted line Z, as hereinabove described.

It is, therefore, Obvious that applicant has provided in his modifiedstructure a control means for insuring a coffee brew to be first broughtup to its brewing temperature, and then, upon the operation of thecontrol means by an operator, for maintaining such brewed coflee at thedesired serving temperature.

It is further obvious that with the structure as set forth herein, it ispossible to ensure a predetermined infusion period during the coffeemaking cycle so as to obtain uniform and satisfactory results whenbrewing cofiee.

While this invention is shown in but two forms, it will be obvious tothose skilled in the art that it is not so limited but it is susceptibleto various other changes and modifications without departing from thespirit thereof and it is desired, therefore, that only such limitationsshall be placed thereon as are specifically set forth in the appendedclaims.

I claim as my invention:

1. In a coffee maker having a heating element, the combination of athermostatic structure responsive to the heat produced by the elementfor regulating the operation of said element to first supply a cofieebrewing temperature and then to automatically reduce the heat producedby said element to maintain the cofifee at a serving temperature belowthe brewing temperature, said thermostatic structure comprising a firstdevice responsive to the heat produced by said element for maintainingenergization of the heating element to produce a high heat output for apre determined period, and aise'cond device also responsive to the heatproduced by said element for maintaining the energization of the heatingelement to produce a low heat output whereby the temperature of the brewis automatically retained at a serving temperature somewhat below thebrewing temperature.

2. In a coffee maker having a heating element, the combination of athermostatic structure responsive to the heat produced by the elementfor regulating the operation of said element to to first supply a cofieebrewing temperature and then to automatically reduce the heat producedby said element to maintain the coilee at a serving temperature belowthe brewing temperature, said thermostatic structure comprising a firstbimetallic element responsive to the heat produced by said element andhaving a closing temperature lower than the serving temperature of lowheat output whereby the temperature of the brew is automaticallyretained at a serving temperature below the brewing temperature.

8. Inacofleemakerhavingaheatingelement. the combination of athermostatic structure responsive to the heat produced by the elementfor regulating the operation of said element to first supply a cofieebrewing temperature and then to automatically reduce the heat producedby said element to maintain the coiiee at a serving temperature belowthe brewing temperature, said thermostatic structure comprising a firstbimetallic element responsive to the heat produced by said element andhaving a closing temperature lower than the serving temperature of thebrew and an adjustable opening temperature for maintaining theenergization of the heating element to'produce a high heat output for apredetermined period, and a second bimetallic element responsive to theheat produced by said element and having a mean operating temperatureintermediate its closing and opening value for intermittentlymaintaining the energization of the heating element to produce a lowheat output whereby the temperature of the brew is automaticallyretained at a serving temperature below the brewing temperature.

4. In a coflee maker having a heating element, the combination or athermostatic structure responsive to the heat produced by the elementfor regulating the operation of said element to first supply a coffeebrewing temperature and then to automatically reduce the heat producedby said element to maintain the coffee at a serving temperature belowthe brewing temperature, said thermostatic structure comprising a firstbimetallic element responsive to the heat produced by said element andhaving a closing temperature lower than the serving temperature of thebrew and a selectively adjustable opening temperature for maintainingthe energization oi the heating element to produce a high heat outputfor a predetermined period, a second bimetallic element responsiveto'the heat produced by said element and having a mean operatingtemperature intermediate it's closing and opening value forintermittently maintaining the energization of the heating element toproduce a low heat out put whereby the temperature of the brew isautomatically retained at a serving temperature below the brewingtemperature, and means for selectively adjusting the opening temperatureof the first bimetallic element in accordance with the quantity ofcoflee to be brewed whereby the length of the initial heating periodwill be of the desired time for a given quantity of coiIee so as toinsure uniiorm results.

5. In a coflee maker having a heating unit and liquid containing vessel,the combination oi a heating stand for retaining said unit, said standhaving a plurality of apertures therein for enabling air to passtherethrough and under and upwardly past said unit and in contact withthe bottom and sides thereof, said vessel being retained upon and incontact with the unit during the infusion period whereby said periodwill be, reduced to a minimum due to the vaporization of liquid in thevessel and the passage of air about the heating unit.

6. In a coffee maker having a heating unit and a liquid-containingvessel, the combination of a heating stand for retaining said unit, saidstand embodying a plurality of apertures therein for enabling air topass therethrough and under andupwardlypastsaidunitandincontactwiththebottom and sides thereoi, and an upstanding peripheral flange portion,said vessel being retained upon and in contact with the heating unit andspaced inwardly from the peripheral flange portion of said stand duringthe infusion period whereby said period will be reduced to a minimum dueto the vaporization of liquid in the vessel and the passage of air aboutthe heating unit and along the lower portion of said vessel.

7. In a coffee maker including a liquid-containing vessel, thecombination of a heating unit,

a stand for supporting said unit embodying a central portion havingapertures therein and an upstanding shoulder about the outer edgethereoi, means for retaining the heating unit a spaced distance upwardlyfrom said central portion and inwardly from the shoulder to permit thepassage of air upwardly through said stand along the bottom andperiphery oi the heating unit, said vessel being retained upon and incontact with the heating unit and spaced inwardly from the upstandingshoulder of said stand whereby the air passing through said stand andalong said heating unit will pass along said vessel so as to rapidlycool the heating unit and vessel due to the vaporization of liquids inthe vessel.

KENNETH L. WOODMAN.

